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Accessory minerals like zircon, rutile and monazite are routinely studied to inform about the timing and nature of geological processes. These studies are underpinned by our understanding of the transfer processes of trace elements and the assumption that the isotopic systems remain undisturbed. However, the presence of microstructures or Pb-bearing phases in minerals can lead to the alteration of the Pb isotopic composition. To gain insight into the relationship between Pb isotopic alterations from inclusions and microstructures, this study focused on inclusions from an ultra-high-temperature metamorphic rutile. The studied inclusions are submicrometer monazites, a common mineral rich in Pb but normally not present in rutile. The sample is sourced from Mt. Hardy, Napier Complex, East Antarctica, an ultra-high-temperature (UHT) metamorphic terrane. By applying correlative analytical techniques, including electron backscatter diffraction mapping, transmission electron microscopy (TEM), and atom probe tomography, it is shown that monazite inclusions are often in contact with low-angle boundaries and yield no preferred orientation. TEM analysis shows the monazite core has a mottled texture due to the presence of radiation damage and nanoclusters associated with the radiation damage defects that are rich in U, Pb, and Ca. Some monazites exhibit a core-rim structure. The rim yields clusters composed of Ca- and Li-phosphate that enclose Pb nanoclusters that are only present in small amounts compared to the core, with Pb likely diffused into the rutile-monazite interface. These textures are the result of two stages of Pb mobility. Initial Pb segregation was driven by volume diffusion during UHT metamorphism (2500 Ma). The second stage is a stress-induced recrystallization during exhumation, leading to recrystallization of the monazite rim and trace element transport. The isotopic signature of Pb trapped within the rutile-monazite interface constrains the timing of Pb mobility to ca. 550 Ma. [ABSTRACT FROM AUTHOR]

In situ age and trace element determinations of monazite, rutile and zircon grains from an ultrahigh temperature (UHT) metapelite‐hosted leucosome from the Napier Complex using laser split‐stream analysis reveal highly variable behaviour in both the U–Pb and trace element systematics that can be directly linked to the microstructural setting of individual grains. Monazite grains armoured by garnet and quartz retain two concordant ages 2.48 and 2.43 Ga that are consistent with the previously determined ages for peak UHT metamorphism in the Napier Complex. Yttrium in the armoured grains is unzoned with contents of ~700 ppm for the garnet‐hosted monazite and in the range 400–1,600 ppm for the monazite enclosed within quartz. A monazite grain hosted within mesoperthite records a spread of ages from 2.43 to 2.20 Ga and Y contents ranging between 400 and 1,700 ppm. This grain exhibits core to rim zoning in both Y and age, with the cores enriched in Y relative to the rim and younger ages in the core relative to the rim. A monazite grain that sits on a grain boundary between mesoperthite and garnet records the largest spread in ages—from 2.42 to 2.05 Ga. The youngest ages in this grain are within a linear feature that reaches the core and is connected to the grain boundary between the garnet and mesoperthite; the oldest ages are observed where monazite is in contact with garnet. Yttrium in the grain is enriched in the core and depleted at the rim with the strongest depletions where monazite is adjacent to grain boundaries between the silicate minerals or in contact with garnet. The unarmoured monazite grains have lower intercept ages of 1.85 Ga, which overlaps with the bulk of ages determined from the rutile and is coincident with a previously reported zircon age obtained through depth profiling from the Napier Complex. The age and chemical relationships outlined above illustrate decoupling between the geochemical and geochronological systems in monazite. Individual grains are suggestive of a range of processes that modify these systems, including volume diffusion, flux‐limited diffusion and fluid‐enhanced recrystallization, all operating at the scale of a single thin section and primarily controlled by host mineral microstructural setting. These findings illustrate how the development of simple partitioning coefficients (cf. garnet/zircon) and geospeedometry based on experimentally determined diffusion coefficients on grain separates may not be achievable. However, it highlights the utility of combining age and trace element concentrations from multiple accessory minerals with microstructural information when trying to build a complete history of tectonothermal events experienced by an ancient rock system that has undergone a prolonged history of thermal, deformational and fluid flow events. [ABSTRACT FROM AUTHOR]

This study integrates Remote Sensing data, field investigation, and petrography to analyze the Zawar Pb–Zn sulfide deposits, in the Paleoproterozoic Aravalli Supergroup rocks of NW India. Structural features of the study area are delineated using Remote Sensing and Shuttle Radar Topography Mission (SRTM) data. Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) data, is used to distinguish the major rock types and alteration zones. Our findings reveal that the Zawar belt is composed of phyllite, quartzite, carbonate, and, greywacke. Phyllites from the hinge of the Main Zawar Fold (MZF) provide critical insights into the distribution of monazite veins, and, support the evidence of hydrothermal alteration over the hinge area of the MZF. Textural evidence investigated by Scanning Electron Microscopic study (SEM) suggests that the monazite is of epigenetic hydrothermal origin, formed subsequently after the formation of the primary host rock. Energy Dispersive X-ray spectroscopic (EDS) study indicates that these monazites have an average composition, P2O5(17.85 wt.%), Ce2O3 14.49, La2O3 6.98, Nd2O3 5.39 and ThO2 1.60 wt.%, suggesting its hydrothermal origin. [ABSTRACT FROM AUTHOR]

A protocol for the monazite (LREE,Y,Th,U,Si,Ca)PO4 in situ Th-U-Pb dating by electron probe microanalyser (EPMA) involves a suitable reference monazite. Ages of several potential reference monazites were determined by TIMS-U-Pb isotope analysis. The EPMA protocol is based on calibration with REE-orthophosphates and a homogeneous Th-rich reference monazite at beam conditions of 20 kV, 50 nA, and 5 µm for best possible matrix matches and avoidance of dead time bias. EPMA measurement of samples and repeated analysis of the reference monazite are performed at beam conditions of 20 kV, 100 nA, and 5 µm. Analysis of Pb and U on a PETL crystal requires YLg-on-PbMa and ThMz-on-UMb interference corrections. Offline re-calibration of the Th calibration on the Th-rich reference monazite, to match its nominal age, is an essential part of the protocol. EPMA-Th-U-Pb data are checked in ThO2*-PbO coordinates for matching isochrones along regressions forced through zero. Error calculations of monazite age populations are performed by weighted average routines. Depending on the number of analyses and spread in ThO2*-PbO coordinates, minimum errors <10 Ma are possible and realistic for Paleozoic monazite ages. A test of the protocol was performed on two garnet metapelite samples from the Paleozoic metamorphic Zone of Erbendorf-Vohenstrauß (NE-Bavaria, western Bohemian Massif). [ABSTRACT FROM AUTHOR]

The Qinling orogen in central China contains several black shale-hosted gold deposits, but the age of their formation and a possible relation between gold mineralization and regional tectonism remain undetermined. Here we present results of in situ monazite U-Th-Pb dating and sericite Rb-Sr dating of the Xiajiadian black shale-hosted gold deposit to provide tight constraints on the time of gold deposition and information on the tectonic setting under which the deposit formed. The Xiajiadian gold deposit is mainly hosted in black shales of the Lower Cambrian Shuigoukou formation, with minor ores contained in sandy conglomerate of the Lower Devonian Xichahe formation. Gold ores in the black shales have been intensively oxidized and consist mainly of hematite, goethite, gypsum, quartz, calcite, native gold, and unrecognized iron oxides. However, gold ores in the sandy conglomerate are free of oxidation and thus provide an opportunity to date the formation of the Xiajiadian gold deposit. The ores consist of pyrite, marcasite, sericite, and quartz, which are associated with a variety of accessory minerals, including monazite, apatite, and titanite. Gold is mainly present as structure-bound ions or nanoparticles in pyrite and marcasite, but minor native gold grains also occur as inclusions in pyrite. Monazite is well developed in the ores, and has close textural association with Au-bearing pyrite and marcasite. Most monazite grains have zoned textures consisting of a core area (Mnz1) and an overgrowth zone (Mnz2). Mnz1 contains 4.8–13 wt.% ThO2 and shows large variations in HREE and prominent negative Eu anomalies in the chondrite-normalized REE patterns. It yields common lead-corrected 208Pb/232Th dates ranging from 910±10 to 416±4 Ma (2σ). These dates are interpreted in terms of a detrital origin for monazite in the core area. Mnz2 has much lower ThO2 contents of 0.8–1.7 wt.% and shows weak negative Eu anomalies in the chondrite-normalized REE patterns. It yields common lead-corrected 208Pb/232Th dates of 229–209 Ma (2σ) with a weighted mean of 217.6±3.0 Ma (2σ), which is considered as the time of Mnz2 crystallization. Sericite in gold ores and associated alteration zones has close relations to Au-bearing pyrite and marcasite, and yields a well-defined Rb-Sr isochron age of 222.2±3.3 Ma (2σ). The sericite Rb-Sr age is indistinguishable within analytical errors from the weighted mean Th-Pb age of Mnz2. The age data presented here indicate that the Xiajiadian gold deposit formed at ca. 220 Ma in the Late Triassic (Norian). We therefore suggest that gold mineralization at Xiajiadian occurred during the transitional stage from oceanic subduction to continental collision that led to the formation of the Qinling orogen. During this stage, metamorphic devolatization of the underlying Early Paleozoic to Proterozoic carbonaceous sequences likely supplied ore fluids from which the Xiajiadian gold deposit formed. [ABSTRACT FROM AUTHOR]

Spodumene‐bearing pegmatite dyke swarms have recently been discovered in the Chaqiabeishan area, at the northeastern margin of the Qinghai‐Tibet Plateau in northwest China. In order to elucidate the connection between the Chaqiabeishan lithium pegmatites and Triassic magmatism and mineralization within the West Kunlun – Songpan ‐Garzê rare‐metal belt, this study presents new columbite‐group mineral and monazite U–Pb dating results, mineral chemistry, monazite in situ Nd isotope analyses and gamma‐ray spectrometric measurements. Magmatism and mineralization at Chaqiabeishan mainly occurred ca. 216 Ma, and the mineralized pegmatites (Mn‐rich columbite‐group minerals, highly evolved monazite compositions and high effective uranium contents in the gamma‐ray survey) were generated from the high degree of the fractional crystallization in a volatile‐rich granitic magma. The source material of the Chaqiabeishan lithium pegmatites (εNd(t) values from −14.4 to −12.8) was more enriched than that of other pegmatite‐type lithium deposits (Jiajika and Bailongshan) in the West Kunlun – Songpan – Garzê rare‐metal belt and is ascribed to melting of ancient crustal materials in the basement. These late‐Triassic mineralizing events were closely related to the collision‐related tectonic setting at the northeastern margin of the Tibetan‐Qinghai Plateau, a product of Paleo‐Tethys Ocean closure. [ABSTRACT FROM AUTHOR]

In view of the problems that alkali to solanite concentrate turned red and acid soluble slurry thickened into foam during comprehensive recovery, which led to product discoloration and decreased production capacity, scanning electron microscopy(SEM) and infrared spectrum analysis were used to analyze the composition of ore pollutants, and the removal effect of calcination method on monazite concentrate contaminants were studied through condition test and pilot plant tests. The results show that the alkali transformation color is mainly caused by the organic matter containing carboxyl group, benzene ring or cycloalkane covering the monazite surface. Under the conditions of calcination temperature of 400 °C and calcination time of 40 min, the COD removal rate of alkali to pulp is greater than 94%, and the organic matter removal effect is good, which can solve the problem of 30% reduction in production and processing capacity, reduce power consumption and energy consumption, remove occupational health and other safety and environmental risks caused by fluting in production, and ensure the recovery rate of uranium and rare earth. This method improves the processing process of monazite and has a certain popularization value. [ABSTRACT FROM AUTHOR]

Leaching of uranium, thorium and rare earth from the monazite selective solution residue were studied by conventional leaching--two-stage countercurrent leaching was studied. The effects of various factors on the leaching was investigated. The results show that the leaching rates of uranium, thorium and rare earth are 98.66 %, 95.37 % and 64.23%, respectively under suitable conditions using conventional leaching method. Using the two-stage countercurrent leaching method, the leaching rates of uranium, thorium and rare earth can be increased by 0.5%~1.0%, the residual acid of the leaching solution can be reduced by more than 50%, and the solid-liquid separation performance of the slurry can be improved to a certain extent. [ABSTRACT FROM AUTHOR]

The geologic evolution of the Gondwanide orogen recorded during the late Palaeozoic along the Panthalassan border of Gondwana is related to an active continental margin, though it is still debatable whether it was built by collision or accretion. To disentangle its orogenic processes and provide constraints on the orogen type, we characterize the physicochemical conditions of metamorphism and associated deformation of the Mina Gonzalito Metamorphic Complex from northern Patagonia (41°28’30” S-65°40’30” W). New field mapping and comprehensive petrochronologic analysis constrain the evolution of a thick-skinned fold and thrust belt in a retroarc setting, which is spatially and temporally related to the geometry and kinematics of the right-lateral reverse El Jagüelito ductile shear zone. Metamorphic evolution resulted in a clockwise P‐T‐t-D path reflecting three stages of continuously changing P-T conditions under high-pressure (8.0–9.9 kbar) amphibolite facies (540–680°C) during a single-phase progressive ductile deformation event. Monazite ages ranging from 303 ± 5 to 252 ± 6 Ma account for the single-phase regional tectono-metamorphic event spanning ~ 50 My. Our results, integrated with regional data, led to interpreting the late Palaeozoic Gondwanide orogen developed along the Panthalassan margin of Gondwana as accretionary in advancing-mode. [ABSTRACT FROM AUTHOR]

High- to ultrahigh-pressure (HP–UHP) rocks recording high-temperature (HT) > 700 °C are well exposed in the Central Alps, making it an ideal region to study the timing of metamorphic stages and the mechanisms of deep-seated rocks exhumation. Here, we report an integrated dataset of petrological and U–(Th–)Pb dating of metapelites surrounding ultramafic lenses from the Cima Lunga unit. At the interface with ultramafics preserving (U)HP–HT assemblages (1.5–3.1 GPa, 650–850 °C), metapelites record higher P‒T values (1.3–2.7 GPa, 700–850 °C) and traces of partial melting, whereas the rest of the unit is dominated by amphibolite-facies conditions. U–Th–Pb dating on zircon and monazite from migmatites indicates that partial melting was episodic involving at least two stages at ~38 to 35 Ma and 33–30 Ma, respectively. While the 38–35 Ma stage matches the HP conditions (> 1.5 GPa) and it is recorded around only one lens with scarce volumes of melt, partial melting at 33–30 Ma is witnessed at lower pressure (~1 GPa) and more widely distributed around the lenses, as within the major shear zones. Far from the ultramafics, zircon from the amphibolite-facies metasedimentary rocks record inherited pre-Variscan ages, while monazite ages at ~22 Ma document mineral growth during the Barrovian cooling. Field and petro-chronological evidence highlight that multiple episodes of partial melting locally developed at the rheological interface promoted by the interplay of fluids extracted from the ultramafic lenses associated with shear heating. New evidence suggests that local variation of P‒T equilibria play a significant role during the exhumation history. [ABSTRACT FROM AUTHOR]

Carbonatite hosts the most important rare earth resources in the world, but the precise timing, ore-forming history, and mechanism of rare earth mineralization in carbonatite systems are still in debate. Here, we report a rare corona texture of monazite-allanite-fluorapatite from the Huangjiagou carbonatite in the Lesser Qinling of central China, and demonstrate that the U-Th-Pb dating, trace elements, and Sr-Nd isotopes of these minerals in the corona are useful tools to unravel multiple-stage events for rare earth element (REE) mineralization and mobilization. The first mineralization event took place at ca. 219 Ma as revealed by the monazite U-Pb age, the same as regional carbonatite forming ages, but the Th-Pb age has been disturbed, which shows a negative correlation with Th contents. The second mineralization event occurred at ca. 128 Ma, as revealed by in situ U-Pb dating of allanite, coeval with the intrusions of neighboring I-type granite. The initial Sr-Nd isotope ratios of allanite show a downtrend from the center to the rim of monazite-allanite-apatite coronas to approach the ratios of neighboring granite, indicating an increasing effect by the metasomatism of magmatic-hydrothermal fluids during the growth of these REE-mineral coronas. Therefore, a two-episode REE mineralization was recognized with the replacement of ca. 219 Ma monazite by ca. 128 Ma allanite-apatite coronas on the function of magmatichydrothermal fluid metasomatism, and this process accompanies the disturbance of Th/Pb geochronology in monazite. Allanite as the product of monazite dissolution can represent the later-stage REE mineralization tracing the REE reworking processes under the hydrothermal conditions in carbonatite systems. Our study highlights the implication of monazite-allanite-fluorapatite coronas on the REE remobilization and mineralization in carbonatite systems. [ABSTRACT FROM AUTHOR]

The article provides generalized data on the geological structure, the results of laboratory analyzes of the heavy fraction of the main placer-forming minerals of the Vovchansk zircon-rutile-ilmenite deposit, which was being developed by Demurinsky Mining and Processing Plant LLC in 2002. The geological structure of the Vovchansk deposit includes a complex of Precambrian rocks of the crystalline basement, the Paleozoic-Cenozoic weathered crust, the Paleozoic-Cenozoic sediments, and Quaternary deposits. The industrial concentration of heavy minerals is confined to the middle and upper parts of the Middle Sarmatian subsuite of the Neogene, composed of fine-grained, essentially quartz sands, with a total thickness of 0.4 to 63 m. The content of heavy minerals in the ore-bearing horizon of the deposit ranges from 93.8 to 485 kg/m³ (ilmenite from 37.6 to 242.6 kg/m³, rutile from 15.9 to 64.6 kg/m³, zircon from 2.9 to 9.4 kg/m³, sillimanite and disthene from 20.4 to 117.5 kg/m³). The content of major and minor elements-impurities in individual minerals of the ore-bearing horizon (178 grains) was determined: ilmenite (18 samples), rutile (40 samples), zircon (35 samples), sillimanite (30 samples), staurolite (25 samples), tourmaline (12 samples), ganite (8 samples), monazite (10 samples). The conducted research clarified the typomorphic features of minerals from the sands of the Vovchansk deposit, established their absolute age and probable original sources. [ABSTRACT FROM AUTHOR]

The Petrivsky iron ore deposit is located on the left bank of the Ingulets River, southeast of the village Petrovo, Oleksandriysky district, Kirovohrad region. Until recently, the deposit was developed of the quarry method. The quarry revealed an iron ore stratum composed of ferruginous quartzites and crystalline schists, and strongly schis-tulated gneisses, ore-free quartzites and carbonate rocks occur in sharply subordinate quantities. In some areas of the quarry, the crystalline slates are partially migmatized, and the bundles of ferruginous quartzite are in many places dissected by veins of aplito-pegmatoid granites and pegmatites. According to the nature of the section, the iron ore stratum belongs to the Artemivska suite of the Ingulo-Ingulets series. Optical microscopy methods revealed heterogeneous cores of relict (clastogenic) zircon within the accessory zircon crystals from gneiss, which made it possible to make an assumption about its primary sedimentary nature, and rather high isotopic ratio 87Sr/86Sr = 0.70914 ± 0.00005 in calcite from calciphyre indicates on sediment accumulation in a basin isolated from the world ocean According to the results of uranium-lead isotope dating of different-grained monazite samples (TIMS method), the granites dissect the iron ore stratum of the Petrivske deposit were rooted in the Paleoproterozoic: aplito-pegmatoid granite 2033.3 ± 2.3 million years ago and plagiopegmatite — 2028.5 ± 5.6 million oyears ago. It is proposed to take the age of 2030 million years as the upper age limit of the iron ore stratum. [ABSTRACT FROM AUTHOR]

The stratiform and vein-hosted Kapunda Cu deposit in South Australia contains a saprolitized hydrothermal vein with 12.37 wt.% total rare earth oxide (TREO). The vein was analyzed by X-ray diffraction, scanning electron microscopy, synchrotron-based X-ray fluorescence microscopy and electron backscatter diffraction to understand the controls that govern high-grade REE accumulation during periods of intense weathering. Petrological assessments indicate the transformation of an apatite-calcite-aluminosilicate-bearing protolith to a supergene assemblage of Fe-oxides, kaolinite and REE-phosphate minerals that include rhabdophane-(Ce), monazite-(Ce) and florencite-(Ce). This transformation was facilitated by progressive acidification of the weathering fluid, which is indicated by: 1) the increasing crystallinity of authigenic Fe-oxides and kaolinite, which led to REE desorption; 2) the textural evolution and increase in grain size of authigenic REE-phosphates from nanoscopic crystallites, to acicular needles, to micro-scale hexagonal prisms; 3) the late dissolution of REE-phosphates; and 4) the replacement of goethite by jarosite, whose sulfate component originated from the oxidation and weathering of proximal sulfide minerals. Alongside the depletion of pH-buffering carbonate minerals that are indicated by the preservation of calcite menisci, this sulfide dissolution also facilitated acid generation. Results illustrate how highly acidic weathering fluids might facilitate either REE mobilization or REE accumulation in regolith. High-grade REE accumulation under acidic supergene conditions is prioritized when the host-rock contains a significant source of depositional ligands (i.e., phosphate in the form of apatite) that can be readily leached during intense weathering. Exploration companies should therefore assay routinely for REEs in any heavily weathered phosphatic rock, due to the observed efficiency of phosphate minerals as geochemical traps for REE accumulation. [ABSTRACT FROM AUTHOR]

The purpose. The aplitoid biotite granites with traces of rheomorphic transformations lying among gneisses and crystalline schists of the Central-Priazovska series of the Ukrainian shield, as well as the anatomy of accessory crystals of zircon and monazite from these granites, were researched. Method. The time of granite intrusion was determined by the uranium-lead isotope dating method based on multi-grain measurements of accessory monazite. The anatomy of zircon crystals was studied in artificial slices by optical microscopy methods. The results. The age of monazites was determined by multigrain weighing based on the 207Pb/206Pb isotopic ratio. The interest in these granites is related to the fact that they form a vein that breaks through the gneisses and crystalline slates of the Сentral-Priazovska series, discovered by the Oldcrimean granite quarry. The structure of the granite is heterogeneous, with grain sizes ranging from 0.1 to 3.5 mm. Based on the ratio between mineral grains and their shapes, the structure is identified as allotriomorphic and flattened. The configuration of the grains and their relationships indicate the coexistence of relict primary magmatic structure with dynamoblastic and brittle-plastic features caused by rheomorphism. These elements include granuloblastic phenomena and the flattening of quartz crystals; granuloblastesis of primary plagioclase grains; myrmekitization of early and crystallization of newly formed feldspars; microclinization of relict orthoclase and crystallization of newly formed microcline, and deformation of biotite flakes. Currently, the granites consist of (in %) acidic plagioclase - 30, microcline + orthoclase - 25, quartz - 45, chloritized dark mica - 1-5. Secondary transformations include biotite chloritization, as well as sericitization and pellitization of newly formed plagioclase. Accessory minerals are represented by zircon, monazite, apatite, possibly magnetite, and rutile, which forms during the replacement of biotite by chlorite. Weathering minerals include clay minerals, iron hydroxides, and carbonates. The anatomy of accessory zircon and monazite crystals has been studied. According to mineralogical research, zircon crystals have a complex structure. Zircon in synpetrogenic granites grows on heterogeneous cores of relict zircon, usually in the form of thin shells. A small number of crystals without cores are also present, consisting exclusively of fine-zonal zircon shells.The monazite is represented by two varieties: large (>0.1 mm) brownish-brown, dark brown to nearly black unevenly colored opaque crystals and small light brown, brown-yellow transparent crystals. Scientific novelty and Conclusions. The age of the granite was determined using the uranium-lead isotope method on multi-grain samples of dark opaque monazite crystals. The weighted average age, based on the 207Pb/206Pb isotope ratio, is 1978.8 ± 6 million years. The age obtained from multi-grain samples of light brown and brown-yellow transparent crystals is 1959 ± 18 million years and theoretically represents the minimum timing of rheomorphism processes.

LnPO 4 ·nH 2 O rhabdophane/monazite is an important actinide-bearing material in the back end of the nuclear fuel cycle. In this work, using Nd3+ to simulate trivalent actinides, Ce 0.5 Nd 0.5 PO 4 ·0.667H 2 O rhabdophane was synthesized by the wet-chemistry method in 90 °C and pH = 1 solution. The sintering behavior of associated Ce 0.5 Nd 0.5 PO 4 monazite ceramics was investigated by pressureless sintering and spark plasma sintering (SPS), along with appraising their chemical stability. The results reveal that Ce3+ is successfully replaced by Nd3+ in the rhabdophane lattice, and rhabdophane can transform to monazite with a temperature over 750 °C. SPS can compact the ceramic sample at a lower temperature compared to pressureless sintering even if the grain size is smaller. Adding a pre-sintering process of 900 °C before SPS and pressureless sintering will further improve the density and Vickers hardness of ceramics. For the chemical stability of Ce 0.5 Nd 0.5 PO 4 monazite ceramics, Ce is more likely to be leached compared to Nd, and the ceramics prepared by SPS with a pre-sintering process have the lowest normalized leaching rates, associated with the values of 2.03 × 10−5 g·m−2·d−1 and 0.75 × 10−5 g·m−2·d−1 for Ce and Nd, respectively. [ABSTRACT FROM AUTHOR]

Granulites exposed in high-grade regional metamorphic belts and exhumed as xenoliths in basaltic pipes are considered as window into the deep crust thus play a key role in constraining models of crustal processes and evolution. Here we present a detailed investigation of the tectono-metamorphic history of the two-pyroxene mafic granulite located in the southern region of the Sonapahar area. This involves conducting monazite chemical dating, analyzing petrological and geochemical characteristics, applying geothermobarometry, performing phase equilibria modeling, and tracing a pressure-temperature (P-T) path. Metamorphic P-T conditions estimated for the mafic granulite using conventional thermobarometer and winTWQ shows temperature in excess of 800°C and pressure of about 8.6 kbar, stand for high temperature granulite facies metamorphism. The metamorphic evolution path obtained from P-T pseudosection suggest a clockwise P-T evolution path, thus signify isothermal decompression and indicate rapid upliftment. Geochemical study of trace and rare earth elements (REE), suggest protolith is of tholeiite basalt in nature that is derived from back arc basin setting near to subduction zone. Additionally, the analyzed rock was examined using primitive mantle-normalized trace element spider diagram. The results indicate an enrichment in large-ion lithophile elements (Th, U, K, Pb) and a depletion in high field-strength elements (Nb, Ta, Ti). The presence of negative anomalies in Nb and Ti, coupled with elevated values of Th, K, and Pb, suggests the possibility of crustal contamination. Monazite chemical data from the studied rock reveals a peak metamorphism age of 521.3 ± 4.20 Ma, which corresponds to the Kuunga Orogeny in the later phase of global Pan-African collision. [ABSTRACT FROM AUTHOR]

Data indicating the important role of microorganisms in the formation of nodular monazite (NM) (kularite) of the Kular Range, Republic of Sakha (Yakutia), are presented. The NM contains microorganisms (cyanobacteria) replaced by REE-bearing phosphate (monazite) in the form of stromatolitic microedifices, as well as framboidal Fe sulfides in monazite. The Corg isotopic composition of kularite corresponds to biogenic carbon: the δ13С values vary from –22.2 to –22.3‰. [ABSTRACT FROM AUTHOR]

Migmatites and partial melts are exposed in both the lower and upper package of the Higher Himalayan Crystallines (HHC) thrust sheet within the Sikkim Himalayas. Zircon monazite and quartz oxygen isotopic ratios from Yumthang Valley, North Sikkim, and Rathong Chuu, West Sikkim, have been used to identify their sources and equilibrium conditions. Monazites show homogeneous growth, whereas zircons show growth rings. U-Th-Pb data on monazite only indicate the latest metamorphic event. However, zircons show metamorphic rim growth between 36 and 24 Ma over their detrital core with trailing growth from 22 Ma to 15 Ma. Pervasive fluids have been interpreted in coeval development during metamorphism, as shown by monazite and zircon c. 30 Ma. The Th/U ratio of zircon is higher and variable with weak residual zoning in the samples from higher elevations. Quartz–metamorphic zircon oxygen fractionation suggests Teq > 600 °C, while quartz–monazite fractionation shows the same or lower temperatures. Multiple sources of melts in the HHC (even along a single valley) have been observed by δ18O of 7‰ to 10‰ in zircon and 5‰ to 9‰ in monazite. Zircon and monazite generated in the same rock have similar δ18O values. Monazite grown ~20 Ma in the lower elevation sample had a low δ18O, suggesting interaction with an external fluid. [ABSTRACT FROM AUTHOR]

Archean to Palaeoproterozoic basement rocks exposed in the Dunhuang block in NW China were affected by Palaeozoic crustal reworking, as constrained by previous zircon U–Pb geochronological investigations. However, relationships between the Palaeozoic metamorphic ages, P–T evolution and deformational history of the region remain ambiguous. In order to address this issue, P–T–t–D paths of paragneisses from the basement of the Hongliuxia belt in the southern Dunhuang block were investigated. Inclusions in garnet and kyanite from the paragneisses are considered as vestiges of Palaeozoic M1 metamorphism corresponding to initiation of the prograde evolution. The earliest continuous metamorphic fabric is an originally steep N–S striking foliation S2. This fabric was reworked by vertical folds F3 associated with the development of a ubiquitous steep, mainly south‐dipping, E‐W striking axial planar foliation S3. The S2 foliation in paragneisses is mainly associated with Grt–St–Ky–Sil–Bt–Ms–Pl–Qz–Rt assemblages in samples from the western domain and with Grt–Ky–Sil–Bt–Kfs–Pl–Qz–Rt assemblages in samples from the northeastern domain of the Hongliuxia belt. The S3 foliation is associated with Grt–Sil–St–Bt–Ms–Pl–Qz–Ilm assemblages in the western domain and with Grt–Sil–Bt–Ms–Pl–Qz–Kfs–Ilm assemblages in the northeastern domain, followed by growth of chlorite in both domains. Early prograde stage (M1) from 4.0–6.5 kbar and 540–560°C to metamorphic peak (M2a) at 9–10 kbar and ~650–675°C is mainly recorded by paragneisses from the western domain. Subsequent decompression is initially accompanied by heating (M2b) constrained to 6.5–7 kbar and 675–710°C in the western domain, and to 6–6.5 kbar and ~730°C in the northeastern domain, followed by cooling (M3) through 4–6.5 kbar and 550–650°C till late chloritization (late M3). In situ U–Pb dating of monazite combined with monazite trace‐element compositions suggests that prograde evolution (M1) most likely started at c. 406 Ma, peak‐P conditions (M2a) were reached at 400–394 Ma, decompression associated with heating (M2b) took place at 393–391 Ma, and cooling (M3) during exhumation probably lasted from 380 to 354 Ma. The prograde metamorphism probably reflects burial during underthrusting of neighbouring continental basement (the Alxa block or an equivalent) below the Dunhuang block. This event culminated in pure shear thickening (D2a) of the whole supra‐subduction margin followed by minor heating and exhumation (D2b). The D3‐M3 event is interpreted as reflecting exhumation during orthogonal shortening of the system, possibly in response to an independent orogenic cycle. Combined with the available regional data, this study reveals the existence of a complex tectono‐metamorphic evolution for the Dunhuang block characterized by two distinct orogenic phases with (i) the thickening of a previously thinned arc‐back‐arc crust recorded in the northern and central belts at 420–410 Ma in the pro‐wedge side of the active margin (Sanweishan phase), followed by (ii) the 410–390 Ma thickening in the retro‐wedge side (Hongliuxia phase). Such a tectonic evolution of the whole Dunhuang block resembles Andean‐type migration of crustal thickening from the convergent front to hinterlands. The D3‐M3 event, potentially responsible for the juxtaposition of rocks from different geological occurrences and depths, is seemingly independent from this Andean‐type orogenic cycle. [ABSTRACT FROM AUTHOR]

The Dom Feliciano Belt is the South American part of an extensive Neoproterozoic orogenic system that developed during the late Cryogenian–early Cambrian close to the margin of southwest Gondwana. The link of its evolution with the tectonic processes in its African counterpart is still not well understood. P–T estimates, Lu–Hf garnet–whole-rock ages, U–Pb monazite SIMS ages and REE garnet and monazite data from samples of the Porongos and Passo Feio complexes indicate diachronous tectonic evolution of the central Dom Feliciano Belt foreland. Metasedimentary rocks of the eastern Porongos Complex reached previously estimated metamorphic peak conditions of ~ 560–580 °C and 5.8–6.3 kbar at 654 ± 2 Ma, based on Lu–Hf isochron garnet–whole-rock age data. This episode represents an early orogenic thickening in the foreland as a response to the beginning of the transpressive convergent evolution of the belt. The monazite age of 614 ± 6 Ma (U–Pb SIMS) is interpreted as associated with post-exhumation magmatic activity in the foreland and suggests that the eastern Porongos Complex was exhumed sometime between ca. 660 and 615 Ma. The main metamorphic and deformation event in the Porongos Complex's western region occurred at ~ 545–565 °C and 4.3–5.3 kbar at 563 ± 1 Ma (garnet–whole-rock Lu–Hf isochron age). The exhumation of this part of the foreland is dated using monazite crystallising during garnet breakdown and suggests retrograde metamorphism at 541 ± 7 Ma (U–Pb SIMS). The main metamorphic fabric in the Passo Feio Complex further to the west developed at 571 ± 2 Ma (garnet–whole-rock Lu–Hf isochron age) at 560–580 °C and 4.7–6.4 kbar. The western part of the Porongos Complex and the Passo Feio Complex have deformed at similar P–T conditions and apparent geothermal gradients at ca. 570–565 Ma. These regions record a second crustal thickening event in the Dom Feliciano Belt foreland and the orogenic front migration towards the west as a response to the onset of crustal thickening on the African side of this long-lived transpressive orogenic system. [ABSTRACT FROM AUTHOR]

This work presents an integrated structural, kinematic, and petrochronological study of the Monte Grighini dome within the Variscan hinterland–foreland transition zone of Sardinia (Italy). The area is characterised by dextral transpressive deformation partitioned into low- and high-strain zones (Monte Grighini shear zone, MGSZ). Geothermobarometry of one sample of sillimanite-bearing mylonitic metapelite indicates that the Monte Grighini shear zone developed under high-temperature (~ 625 °C) and low-pressure (~ 0.4–0.6 GPa) conditions. In situ U–(Th)–Pb monazite geochronology reveals that the deformation in the shear zone initiated at ca. 315 Ma. Although previous studies have interpreted the Monte Grighini shear zone to have formed in a transtensional regime, our structural and kinematic results integrated with constraints on the relative timing of deformation indicate that it shows similarities with other dextral ductile transpressive shear zones in the Southern European Variscan belt (i.e., the East Variscan Shear Zone, EVSZ). However, dextral transpression in the Monte Grighini shear zone started later than in other portions of the EVSZ within the framework of the Southern European Variscan Belt due to the progressive migration and rejuvenation of deformation from the core to the external sectors of the belt. [ABSTRACT FROM AUTHOR]

To support the role of proximal and remote sensing in geological rare earth element (REE) resource exploration, we studied the reflectance spectroscopy of synthetic single- and mixed-REE phosphate phases. Synthesis yielded monazite for the elements La to Gd, and xenotime for Dy to Lu and Y. Visible-to-shortwave infrared (350–2500 nm) reflectance spectra of synthetic single-REE monazites and xenotimes can be used to identify the ions responsible for the absorption features in natural monazites and xenotimes. Nd3+, Pr3+ and Sm3+ produce the main absorption features in monazites. In natural xenotime, Dy3+, Er3+, Ho3+ and Tb3+ ions cause the prevalent absorptions. The majority of the REE-related absorption features are due to photons exciting electrons within the 4f subshell of the trivalent lanthanide ions to elevated energy levels resulting from spin-orbit coupling. There are small (< 20 nm) shifts in the wavelengths of these absorptions depending on the nature of the ligands. The energy levels are further split by crystal field effects, manifested in the reflectance spectra as closely spaced (∼ 5–20 nm) multiplets within the larger absorption features. Superimposed on the electronic absorptions are vibrational absorptions in the H2O molecule or within [OH]−, [CO3]2− and [PO4]3− functional groups, but so far only the carbonate-related spectral features seem usable as a diagnostic tool in REE-bearing minerals. Altogether, our study creates a strengthened knowledge base for detection of REE using reflectance spectroscopy and provides a starting point for the identification of REE and their host minerals in mineral resources by means of hyperspectral methods. [ABSTRACT FROM AUTHOR]

As a tectonic window into the Lesser Himachal Himalaya, India, a group of metasediments and gneissic rocks, known as the Jutogh Group and Wangtu Gneissic Complex (WGC), occurs near the Jhakri thrust to the west and Wangtu to the east. In the Jutogh Group, chlorite-mica schist, garnet-staurolite schist and sillimanite-schist develop successively. The formation of chemically zoned garnet, which destabilized low-temperature assemblages, is predicted to be at 550–650 °C and 0.8–0.9 GPa by phase equilibria modelling. The retrograde segment consists of exhumation and cooling, yielding a tight clockwise P–T path. Moreover, textural observations and in-situ U-Th-Pb chemical dating indicate that metasedimentary rocks contain Cambrian monazites. These monazites have ages that cluster around 500 Ma. The ƐNd[1.8Ga] of Jutogh rocks ranges from − 1.0 to -8.1, with depleted mantle-model ages between 3.07 and 2.25 Ga. The garnet core and its leachates yield an Sm-Nd isochron age of 472 Ma. Another Sm-Nd isochron age of 454 Ma is obtained from biotite, garnet rim, and garnet rim leachate. According to phase equilibrium modelling, Sm-Nd dating, and monazite geochronology, the Jutogh Group experienced metamorphism along the northeast margin of Gondwana during the Cambro-Ordovician accretion. [ABSTRACT FROM AUTHOR]

Artisanal mining is intensely carried out in developing countries, including Brazil and especially in the Amazon. This method of mineral exploration generally does not employ mitigation techniques for potential damages and can lead to various environmental problems and risks to human health. The objectives of this study were to quantify the concentrations of rare earth elements (REEs) and estimate the environmental and human health risks in cassiterite and monazite artisanal mining areas in the southeastern Amazon, as well as to understand the dynamics of this risk over time after exploitation. A total of 35 samples of wastes classified as overburden and tailings in active areas, as well as in areas deactivated for one and ten years were collected. Samples were also collected in a forest area considered as a reference site. The concentrations of REEs were quantified using alkaline fusion and ICP-MS. The results were used to calculate pollution indices and environmental and human health risks. REEs showed higher concentrations in anthropized areas. Pollution and environmental risk levels were higher in areas deactivated for one year, with considerable contamination factors for Gd and Sm and significant to extreme enrichment factors for Sc. Human health risks were low (< 1) in all studied areas. The results indicate that artisanal mining of cassiterite and monazite has the potential to promote contamination and enrichment by REEs. Highlights: REEs were first assessed in artisanal mines of monazite and cassiterite in the Brazilian Amazon. All anthropized areas showed higher concentrations of REEs. The gratest risk occurred in areas exploited a year ago. REEs pose risks to the environment and human health. [ABSTRACT FROM AUTHOR]

Attempts to geochemically distinguish between metamorphic-hydrothermal systems that form orogenic gold deposits and both reduced and oxidized magmatic-hydrothermal systems using isotopes or metal associations have proven ambiguous, particularly for orogenic gold and reduced intrusion-related gold systems. The absence of conclusive geochemical discriminators and the overlap in geologic characteristics have led to gold deposit models being potentially incorrectly applied, which in turn negatively affect regional mineral exploration and mine planning. In this study, in situ electron microprobe geochemical analyses of hydrothermal monazite and xenotime crystals associated with different types of gold-bearing deposits are shown to be effective geochemical discriminators. There are notable differences in mineral chemistry such as rare earth element (REE) profiles, total light REE, Dy, Er, Pr, Y, Nd/Sm, and La/Sm that distinguish monazite precipitated from metamorphic-hydrothermal fluids that form orogenic gold deposits and those precipitated from magmatic-hydrothermal fluids that form both porphyry Cu-Mo-Au and reduced intrusion-related gold deposits. Notable differences in overall xenotime abundances and concentrations of heavy REEs, Ca, and Sc are distinctive between the different deposit classes for xenotime. The origin of the controversially classified Pogo gold deposit, Tintina gold province, Alaska, which has been characterized as both a reduced intrusion-related and an orogenic gold deposit, is tested based upon the noted chemical differences associated with these hydrothermal phosphates. The findings of this study have implications for exploration and mine development in the Tintina gold province and other areas that contain deposits that are controversially classified as either orogenic or as magmatic-hydrothermal gold deposits. [ABSTRACT FROM AUTHOR]

Monazite is one of the main light rare earth element (REE) minerals and is associated with the presence of Th. This poses challenges in processing due to the strong radiation present in this mineral. However, the use of Th as a nuclear fuel, after the transformation of 232Th into 233U, has been considered a better option than the currently more widespread use of 235U. Therefore, the separation of Th from the REE after leaching is an essential step that requires optimization. In this study, the treatment of a leach solution in a hydrochloric medium from dephosphorized monazite is addressed. The separation of Th from light REEs was performed by solvent extraction with Cyanex 572 or 272. The tests considered included (1) the ratio of the monazite leaching liquor and organic solution, (2) the initial pH values, and (3) the concentration of the extractants. The aqueous-phase samples were analyzed by Inductively Coupled Plasma Optical Emission spectroscopy (ICP-OES). It was observed that at low pH, 60% of the Th was extracted by Cyanex 272 and 90% by Cyanex 572 in one single step. Acidity had little effect on Th extraction. The extractions of light REEs by Cyanex 272 and 572 were negligible in most cases, but for pH values greater than 2, Cyanex 272 extracted a considerable fraction of these elements, which did not occur with Cyanex 572. The results show that Th can be easily separated from light REEs in an acidic and hydrochloric medium by both Cyanex 272 and Cyanex 572. [ABSTRACT FROM AUTHOR]

Distributions of 226Ra, 232Th and 40K were studied in the coastal region of Kanyakumari district, a high background natural radiation area (HBNRA). The absorbed gamma dose rate ranged from 107 ± 11 to 41,126 ± 187 nGy/h. The radiation hazard parameters were found to be much higher than the UNSCEAR world average values. 232Th/226Ra activity ratios ranged from 3 to 45, which indicates the collected sand samples may be rich in Th bearing monazite minerals that are mainly responsible for the enhanced radiation level in the Kanyakumari HBNRA. [ABSTRACT FROM AUTHOR]

The timing of partial melting in high-grade metamorphic rocks is critical for constraining tectonic histories and processes. However, uncertainties exist about the behavior of monazite and zircon during partial melting, especially about the timing of crystallization with respect to melting reactions. This study is focused on a single sample (16TG143) of finely layered, migmatitic gneiss from the Adirondack Highlands, New York, interpreted to have undergone extensive biotite dehydration melting (i.e., Bt + Pl + Als + Qz = Grt + Kfs + melt). The rock contains one distinct leucosome layer. The non-leucosome (gray gneiss) portion of the migmatite has millimeter-scale sublayers with distinct differences in modes and mineralogy. The layers are interpreted to reflect the differential preservation of reactants and products formed during the forward and reverse progress of the melting reaction. Monazite and zircon modes, and to some degree, texture, composition, and geochronology all vary from layer to layer. Both minerals have up to three domains: ca. 1150 Ma anhedral cores, ca. 1050 Ma monazite mantles/fir tree textured zircon, and ca. 1030 Ma rims. The heterogeneous layered gray gneiss provides robust constraints on the timing of melting (ca. 1050 Ottawan orogenesis), melt crystallization, and post-melting retrogression, in addition to information about earlier metamorphic events. Early-formed monazite and zircon grains were largely dissolved during progressive melting, except where preserved as relicts or inclusions. Monazite mantles and fir tree zircon grains precipitated upon cooling during progressive melt crystallization between temperatures of 800 and 750 °C. Rims are interpreted to have precipitated during subsolidus, solid-state retrogression after ca. 1050 Ma. Correlations between the gneissic layering, melting reactions, and the character of geochronometers emphasize the importance of characterizing the layer-forming and chronometer petrogenesis processes as a critical part of deconvoluting the history of migmatitic gneisses. [ABSTRACT FROM AUTHOR]

The mobility of trace elements in supercritical fluid-melt derived from pelite rich in volatiles has been studied experimentally at pressures from 3.0 to 7.8 GPa and temperatures from 750 to 1090 °С using the diamond trap method. The experiments simulate the conditions of warm and hot subduction, in which pelite either retains the whole inventory of volatiles or releases a fluid in three successive devolatilization steps. The 3.0 GPa and 750 °С runs with pelite rich in volatiles yield a supercritical fluid (SCF) which attains equilibrium with an eclogitic residue bearing phengite and accessory rutile, zircon, and monazite. At ≥5.5 GPa and ≥850 °С, above the second critical endpoint, the SCF transforms into a supercritical fluid-melt (SCFM) which acquires higher concentrations of almost all incompatible trace elements while the mineral assemblage of the equilibrium eclogitic residue remains the same but lacks monazite. The trace-element enrichment of SCFM is most prominent for Ba, Sr, LREE, Th, and U. At the hot subduction conditions, the fluid-melt likewise contains more K, Rb, Zr, and Hf, though LREE contents become lower. The negative Nb anomaly persists in all cases. SCFM has its trace-element composition generally similar to that of hydrous melt derived from oceanic sediments, but contains more REEs and water. Partitioning of LILE, HFSE, and LREE between the SCFM and residue phases mainly depends on the fluid-melt fraction and stability of host phengite, monazite, zircon, and rutile. Thus, sediment-derived SCFM can carry both fluid-mobile and sediment-melt elements to regions of arc- and back-arc magma generation and can translate the negative Nb anomaly inherited from sediment into the magmas. Early devolatilization of pelite increases the stability of monazite and phengite in the residue and provides efficient LREE, K and Rb transport to the mantle depths of ~ 250 km. Effective LREE and Th depletion of UHP metamorphic rocks is possible by SCFM release near peak metamorphic conditions. [ABSTRACT FROM AUTHOR]

Simultaneous U–Pb and U–Th dating using laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) was performed on the ca. 0.1 Ma Toya tephra and the ca. 0.08 Ma SS14-28 U–Th zircon reference material. In U–Pb dating, both Th/U and Pa/U partitioning between magma and minerals were considered. In U–Th dating, both abundance sensitivity and molecular interferences on 230Th were reevaluated. As a result, the Toya tephra yielded an accurate weighted mean U–Pb age of 0.103 ± 0.029 Ma (2σ) using zircon and monazite. Conversely, the SS14-28 zircon yielded an inaccurate U–Pb age (0.25 ± 0.10 Ma), which was attributed to low 206Pb signal intensity. Both the Toya tephra zircon and the SS14-28 zircon yielded accurate U–Th model ages of 0.108 ± 0.014 Ma and 0.078 ± 0.007 Ma, respectively. The agreement of U–Pb and U–Th ages for Toya indicates that simultaneous U–Pb and U–Th dating is possible and viable. The inappropriate age of SS14-28 U–Pb age and appropriate U–Th model age also indicates it is preferable to apply both U–Pb and U–Th dating simultaneously for young (<0.4 Ma) zircons to check internal consistency. The proposed double dating approach may be especially useful for small grains when it otherwise would be impossible to obtain multiple ages from a single grain. By adopting simultaneous U–Pb and U–Th dating using LA-ICP-MS, zircon crystallization ages as old as 4.5 Ga to as young as 0.1 Ma (or even younger) can be obtained in a quick and cost-effective manner with a reasonable (~5% at 1σ) uncertainty. [ABSTRACT FROM AUTHOR]

New U–Th–Pb chemical data from both electron probe microanalysis and U–Pb laser ablation-inductively coupled plasma mass spectrometry on monazite inclusions in giant andalusite porphyroblasts indicate that the lowermost subdivision of the Rocky Cape Group in northwest Tasmania underwent metamorphism at ca 1100 Ma. The Proterozoic Rocky Cape Group is a ∼10 km-thick succession of quartz arenite, siltstone and pelite. These sediments were deposited between ca 1450 and ca 1010 Ma. Metamorphism within the Rocky Cape Group ranges from the prehnite–pumpellyite to upper greenschist facies, locally reaching garnet grade. In the lowermost formation of the Rocky Cape Group, andalusite-bearing mineral assemblages in the Pedder River Siltstone formed prior to or synchronously with monazite development. The andalusite-bearing mineral assemblage indicates relatively low-pressure conditions of <200 MPa, consistent with the stratigraphic thickness of the Rocky Cape Group (∼10 km). However, the presence of the intermediate-temperature biotite–andalusite mineral assemblages (500 °C) in the study area suggests the contribution of additional heat sources. Garnet porphyroblasts were observed ∼2 km away. Similar-age medium-grade metamorphism and magmatism at about 1100 Ma have been observed regionally in the South Tasman Rise and East Tasman Plateau, and in areas that are thought to have been contiguous with northwestern Tasmania such as Dronning Maud Land, central Arizona (Yavapai–Mazatzal) and Belt–Purcell Basin in the southwestern and northwestern Laurentian crustal sequences. The pressure and temperature relationships, mineral associations and regional data suggest additional heat flow was present through the lower part of the Rocky Cape Group. The higher geothermal gradient could be attributed to burial during basin development and deposition of the upper Rocky Cape Group or associated magmatism on the margin of Laurentia during assembly of Rodinia. Low-pressure, intermediate-temperature mineral associations occur in the Rocky Cape Group. Heat sources are unrelated to nearby Devonian granite. Robust ages reveal the first discovery of 1100 Ma metamorphism in Tasmania. These provide data for a missing link in Rodinian paleogeographic reconstructions. [ABSTRACT FROM AUTHOR]

The Anadolian massif (about 300 km2) is located between the rivers Kalmius and Kalchyk (East Azov). It is composed of leucocratic granites in the central part, and on the periphery — granites enriched with dark-colored minerals that turn into migmatites. Granites of the Anadolian massif together with other autochthonous and paraautochthonous essentially difeldspar (spar-predominant) subalkaline amphibole-biotite migmatites, biotite and biotite-muscovite medium- and coarse-grained porphyry-like granites and leucogranites, usually monazite-bearing, are separated in the Anadolian complex. The granites of the complex are spread over almost the entire territory of the Priazov megablock, where they form subconforming vein bodies among the gneisses and crystalline schists of the Central Priazov series, or form the vein material of migmatites developed on metamorphic rocks of the same series. Granites of the Anadolian massif, which are common in the quarry of Myrny, contain accessory zircon, the crystals of which have a complex structure due to the presence of heterogeneous relic cores of substrate rocks on which relatively thin shells of synpetrogenic zircon grow. According to the results of dating of multi-grain samples of monazite by the uranium-lead isotope method, the granites of the Anadolian massif were formed 2047.9±2.2 million years ago. [ABSTRACT FROM AUTHOR]

The community in Central Bangka Regency carried out an increase in illegal mining in 2021, which could potentially threaten the loss of strategic natural resources. Rocking table miners in Central Bangka Regency produce zircon sand, tin sand, monazite, ilmenite, and tailings, which are potential natural resources containing rare earth metal elements. This research aims to analyze the radioactive content of the minerals zircon sand, tin sand, monazite, ilmenite, and tailings as a threat to human health. The research showed that monazite samples from all villages still had a lot of rare earth metals in them, like yttrium (Y), lanthanum (La), cerium (Ce), samarium (Sm), neodymium (Nd), and gadolinium (Gd). The test results showed that monazite had the highest average concentrations of Rare Earth Elements (REEs), with values of 10.27±3% for La, 12.15±3% for Ce, 24.40±3% for Sm, 7.37±3% for Nd, and 0.69±3% for Gd. For tin samples, the average (Ce) was 2.79±3%, zircon samples had an average (Ce) of 4.33±3%, and (Nd) 1.04±3%. In the ilmenite samples, the average value (Y) was 6.64 ± 3%. Monazite has the most rare earth metal elements, but it has a very low selling price. Monazite plays a crucial role in safeguarding and preventing the loss of strategic natural resources and health threats. It provides policy advice to related institutions through various roles and functions, including investigation, early prevention, and forecasting of these threats.

Rare earth metals (REE) constitute one of the most crucial groups of elements globally. In Indonesia, deposits of REE have been recognized within monazite minerals extracted from tin mining operations in Bangka. Nevertheless, Indonesia has not used these deposits and has instead heavily relied on imports from other countries. This study aims to recover rare earth metals, specifically Cerium (Ce), Lanthanum (La), Ytterbium (Yb), and Yttrium (Y), from monazite sand, a by-product of tin mining. The method employed in this research is Mechanochemical Decomposition, involving the reaction of monazite samples with a 33 wt% solid Sodium Hydroxide (NaOH) to convert REE-Phosphate compound into REE-Hydroxide. The process begins with sample preparation, involving mechanochemical decomposition using a ball mill, followed by roasting at 400°C, leaching with distilled water, and subsequent steps of filtration and drying at 120°C. Various initial particle sizes, denoted as +65, -65 +100, -100 +140, -140 +170, and -170 mesh, were used to assess their effect on the recovery and grade of REE. Various initial particle sizes, denoted as +65, -65 +100, -100 +140, -140 +170, and -170 mesh, were used to assess their effect on the recovery and grade of REE. The series of procedures revealed notable improvements in the REE content in monazite. The highest recovery of Ce, La, Yb, and Y elements reached 46.43%, 70.08%, 22.69%, and 23.31%, while the highest grade of those elements obtained the values of 4.116%, 1.543%, 0.263%, and 1.681%, respectively. In alignment with prior research, the recovery of Light Rare Earth Elements (LREEs) surpasses that of Heavy Rare Earth Elements (HREEs). However, a unique observation emerges: a diminishing trend in both recovery and grade as particle sizes become finer. This unexpected phenomenon warrants further investigation to elucidate the mechanisms governing rare earth metal recovery from monazite sand under varying particle sizes.

Mantle rocks usually contain rare earth elements (REEs) in very low concentrations. Here, we document an occurrence of monazite associated with REE-rich apatites in a carbonate-bearing wehrlite xenolith from central Vietnam. The xenolith displays an equigranular matrix of rounded olivine grains while texturally primary orthopyroxene, clinopyroxene and spinel are notably absent. Scattered within the olivine matrix, two types of domains are present: domain-I contains blocky clinopyroxene grains within a matrix of quenched silicate melt and is associated with a second generation of olivine, small euhedral spinel, and rare grains of carbonates. Domain-II contains irregularly shaped patches of carbonate associated with silicate glass, secondary olivine, spinel, and clinopyroxene. Monazite and apatite occur only in domain-I: very small rounded to elongate monazite I grains are included in primary olivine, partly crosscut by fine glass veinlets, monazite II as large grains up to 300 × 200 μm in size and monazite III as small euhedral and needle-like crystals in silicate glass pools. Apatite I forms lath-shaped to rounded crystals up to 200 × 50 μm in size, whereas apatite II is present within silicate melt pools where it forms euhedral needle-like to equant grains. Monazites show compositional variation mainly with respect to ∑REE2O3 (63–69 wt %) and ThO2 (1.1–5.3 wt %) and only minor variations in P2O5 (29–32 wt %), SiO2 (<0.05–0.4 wt %), and CaO (0.2–0.4 wt %). Apatites are characterized by strongly variable and high REE2O3 and SiO2 contents (4–27 wt % ∑REE2O3, 0.6–6.8 wt % SiO2) as well as with significant Na2O (0.3–1.5 wt %), FeO (0.1–1.8 wt %), MgO (0.2–0.6 wt %) and SrO (0.2–0.9 wt %) contents. F and Cl contents are in the range 1.9–3.0 wt % and 0.2–0.8 wt %, respectively. The textures observed in this wehrlite xenolith are thought to be the result of an interaction of depleted (harzburgitic) mantle with cogenetic silicate and carbonatite melts formed by fractionation-driven immiscibility within a parental SiO2 undersaturated melt characterized by high P, CO2, and REE contents. The immiscibility occurred in the shallow subcontinental lithosphere at T of 700–800 °C and a depth of ~30 km and the melt–rock interaction occurred in two successive and most likely nearly simultaneous events: an initial stage of metasomatism was triggered by the P-REE-CO2-rich agent with low aH2O resulting in the co-precipitation of carbonates as patches and along micro-veins and of phosphates in a peridotitic assemblage. A second stage is characterized by pervasive infiltration of an alkali-rich basaltic melt into the carbonate + phosphate-bearing assemblage. Based on 232Th and 208Pb contents of monazite, a young age of ~2 Ma can be calculated for the timing of the monazite-forming metasomatic imprint. Based on 39Ar-40Ar extrusion ages of the xenolith-hosting alkali basalts of 2.6–5.4 Ma, this indicates that both carbonatite and basaltic melt infiltration must have occurred no more than a few hundred thousand years before extraction of the xenolith to the surface. [ABSTRACT FROM AUTHOR]

The atomic-level structure and electronic properties of monazite were investigated using a first-principles method based on density functional theory (DFT). First, the geometric structure of monazite was optimized, followed by calculations of its Mulliken population, electron density, and density of states, which were subsequently analyzed. The findings of this analysis suggest that monazite is highly susceptible to cleavage along the {100} plane during crushing and grinding. When SPA was utilized as the collector, the recovery rate of monazite was higher than that when LF-P8 was used. The zeta potential and adsorption energy results indicated that the zeta potential after SPA adsorption tended towards negativity, and the adsorption energy was smaller, indicating that SPA exhibited stronger adsorption performance. LF-P8 was stably adsorbed on the monazite (100) surface via mononuclear double coordination. SPA was stably adsorbed on the surface of monazite (100) via binuclear double coordination. The results of this study provide valuable insights into the adsorption of monazite by commonly used flotation collectors. These findings are of substantial importance for future endeavors in designing flotation collectors capable of achieving selective monazite flotation. [ABSTRACT FROM AUTHOR]

Rare Earth Elements (REE) phosphates (monazite, xenotime, and rhabdophane) are critical REE-bearing minerals typically formed in hydrothermal and magmatic ore deposits. The thermodynamic properties of those REE minerals are crucial to understanding the solubility, speciation, and transport of REE complexes. However, the standard-state Gibbs free energy of formation (∆G°f) values reported for these minerals in the literature vary by up to 25 kJ mol−1. Here, we present linear free energy relationships that allow the evaluation and estimation of the ∆G°f values at 25 °C and 1 bar for the three minerals from the ionic radius (rREE3+) and the non-solvation Gibbs free energy contribution to the REE3+ aqua ion (∆G°n, REE3+): ∆G°f,monazite − 399.71 rREE3+ = 1.0059 ∆G°n,REE3+ − 2522.51; ∆G°f,xenotime − 344.08 rREE3+ = 0.9909 ∆G°n,REE3+ − 2451.53; and ∆G°f,rhabdophane − 416.17 rREE3+ = 1.0067 ∆G°n, REE3+ − 2688.86. Moreover, based on the new dataset derived for REE end-members, we re-fitted the binary Margules parameter (W) from previous theoretical calculations into linear correlations: W + 0.00204 ∆G°'n,monazite = 39.3549 ∆V + 0.0641; W + 0.00255 ∆G°'n,xenotime = 25.4885 ∆V − 0.0062. The internally consistent thermodynamic properties of these REE phosphates are incorporated into the computer program Supcrtbl, which is available online at Zhu's research website. [ABSTRACT FROM AUTHOR]

U–Pb geochronology of shocked monazite can be used to date hypervelocity impact events. Impact-induced recrystallisation and formation of mechanical twins in monazite have been shown to result in radiogenic Pb loss and thus constrain impact ages. However, little is known about the effect of porosity on the U–Pb system in shocked monazite. Here we investigate monazite in two impact melt rocks from the Hiawatha impact structure, Greenland by means of nano- and micrometre-scale techniques. Microstructural characterisation by scanning electron and transmission electron microscopy imaging and electron backscatter diffraction reveals shock recrystallisation, microtwins and the development of widespread micrometre- to nanometre-scale porosity. For the first time in shocked monazite, nanophases identified as cubic Pb, Pb3O4, and cerussite (PbCO3) were observed. We also find evidence for interaction with impact melt and fluids, with the formation of micrometre-scale melt-bearing channels, and the precipitation of the Pb-rich nanophases by dissolution–precipitation reactions involving pre-existing Pb-rich high-density clusters. To shed light on the response of monazite to shock metamorphism, high-spatial-resolution U–Pb dating by secondary ion mass spectrometry was completed. Recrystallised grains show the most advanced Pb loss, and together with porous grains yield concordia intercept ages within uncertainty of the previously established zircon U–Pb impact age attributed to the Hiawatha impact structure. Although porous grains alone yielded a less precise age, they are demonstrably useful in constraining impact ages. Observed relatively old apparent ages can be explained by significant retention of radiogenic lead in the form of widespread Pb nanophases. Lastly, we demonstrate that porous monazite is a valuable microtexture to search for when attempting to date poorly constrained impact structures, especially when shocked zircon or recrystallised monazite grains are not present. [ABSTRACT FROM AUTHOR]

By studying the various metal ions released from the grinding process, and conducting the flotation test of monazite and symbiotic ore, using zeta potential measurements and FTIR infrared spectrum analysis methods, the influence of metal ions on the surface of monazite and the mechanism of action are obtained. The results showed that the main metal ions in the flotation environment of monazite are Ca2+, Ba2+, and Fe3+. When the pulp pH value was 8, Ca2+, Fe3+, and Ba2+ concentration was 3×10-4 mol/dm³, 3×10-5 mol/dm³, and was 2×10-4 mol/dm³ respectively, and OHA collector dosage was 5×10-4 mol/dm³, while the flotation recoveries of monazite, calcite. And fluorite was above 95 %, 40.43 %, and below 45.32 %, and the recovery rate of barite and bastnaesite in the presence of Ca2+ and Fe3+ is below 54.32 % and 38.68 %, respectively and the effective separation of monazite and symbiotic ore was obtained. The zeta potential measurements showed that when only metal ions are added to monazite, monazite (IEP) shifts to the right, and the negative charge on the surface of monazite decreases, which may be due to the positive charge of metal ions adsorbed on the surface of monazite, increasing the positive charge on the surface of monazite. When Ca2+, Ba2+, Fe3+, and OHA were added to the monazite pulp, the IEP of monazite moved to the left, and the negative charge of monazite shifted to the positive direction as a whole, indicating that Ca2+, Ba2+, and Fe3+ were adsorbed on the surface of monazite and increase the positive charge on the surface of monazite. When the pH value was 7 ~ 10, the surface of monazite was the same as that before and after the action of the agent, and both were negatively charged. At this time, OHA can still adsorb on the calcite, that was, the chemical affinity overcomes the same electric repulsion and adsorbs, so that the potential of the monazite after the action is reduced, which is chemical adsorption. The FTIR showed that when the metal ions Ca2+, Ba2+, and Fe3+ are added to activate the surface of monazite, the peak area of the organic functional group-CH2-CH3 at 3000-2800 cm-1 was enhanced, and a new peak appears at 1382 cm-1. The reason is that the N-O-H functional group of OHA collector was adsorbed on the surface of monazite, and a red shift (44 cm-1) occurs, and a new peak appears at 1454 cm-1. The reason is that the C-N functional group of OHA collector is adsorbed on the surface of monazite. The lone electron pair of the nitrogen atom of the amide group in the OHA forms chelates with Ca2+, Ba2+, and Fe3+ atoms, which further increases the adsorption amount of OHA. This showed that the adsorption of monazite surface by metal ions provides active sites for the adsorption of OHA collectors. These phenomena indicate that the adsorption capacity of OHA on the surface of monazite activated by Ca2+, Ba2+, and Fe3+ is enhanced and a stable five-membered ring metal chelate is formed. Combined with flotation results and zeta potential data, infrared spectroscopy analysis, the adsorption capacity of Ca2+, Ba2+, and Fe3+ activated monazite surface: Fe3+>Ca2+>Ba2+. [ABSTRACT FROM AUTHOR]

The crustal evolution of the southernmost ∼2000–1800 Ma Trans‐Hudson orogen (THO) is enigmatic due to burial by Phanerozoic sediments. We provide new insights through petrochronologic analysis of a paragneiss drill core sample. Detrital zircon age peaks at 2625, 2340, and 1880 Ma and Hf isotopes suggest Paleoproterozoic arc development proximal to Archean source(s). Phase equilibria modeling and ternary feldspar thermometry suggest peak conditions of ≥1 GPa, ≥900°C, the first recognition of extreme, ultra‐high temperature metamorphism in the THO. The largely isobaric P‐T path, rapid heating rate, and ∼20 Myr duration (1872–1850 Ma) of peak conditions suggest that this metamorphism occurred in a back‐arc tectonic setting. The sample records post‐peak (1850–1815 Ma) mid‐crustal residence, slow cooling, and exhumation. Further retrogression occurred during Proterozoic regional exhumation (1630–1470 Ma) and Phanerozoic (360–220 Ma) reheating and/or fluid influx. Evidence for Paleoproterozoic arc(s) supports geophysical data for Archean cratonic and Paleoproterozoic arc crust in this region. Plain Language Summary: The Trans‐Hudson orogeny was a Himalayan‐scale collisional mountain building event approximately 1.8 billion years ago that formed the core of North America. The southern portion of the Trans‐Hudson orogen (THO) is poorly understood because it is almost entirely buried by younger rocks. It is unknown whether the southern THO is underlain by Archean or Proterozoic crust. The timing, conditions, and setting of high‐grade metamorphism in this region are also poorly known. We carried out petrologic, geochemical, and geochronologic analyses on a metasedimentary rock sample recovered from drill core. Detrital zircon and tracer isotopic data show derivation from both Paleoproterozoic and Archean sources. This suggests that Paleoproterozoic magmatic arc(s) developed on or near Archean crust. The rock sample experienced extreme temperatures (≥900°C, ≥1 GPa) and partial melting between approximately 1870 and 1850 million years ago perhaps in a back‐arc tectonic setting. This marks the first recognition of extreme, ultra‐high temperature metamorphism in the THO. Later retrograde metamorphism occurred in the Mesoproterozoic and Phanerozoic. These constraints provide new understanding of the enigmatic southern THO and highlight the ability of a combined petrologic, geochemical, and geochronologic study to extract a comprehensive record of crustal evolution from a single sample. Key Points: Paleoproterozoic arc(s) buried beneath North Dakota developed proximal to, or on, Archean craton(s)Metamorphic temperatures of >900°C are the first recognition of ultra‐high temperature (UHT) metamorphism in the Trans‐Hudson orogenBack‐arc setting for UHT metamorphism indicated by isobaric P‐T path and short timescales of heating and peak conditions [ABSTRACT FROM AUTHOR]